The diagnostic radiographic
approach to pineal tumors has changed over the past 30 years. Skull radiography,
once an important study for detecting possible pineal neoplasm, has fallen into
disuse because of its low sensitivity in detecting tumors. Unless the neoplasm
is calcified, or unless the calcification in the pineal gland is displaced by a
contiguous tumor or hydrocephalus, or unless changes of increased intracranial
pressure are reflected in the sella, sutures, or calvarium, the plain x-ray film
of the skull is not informative. Carotid and vertebral arteriography have been
used in the past to identify the arterial blood supply to the pineal gland,
venous drainage, and vascular displacement due to mass effect and obstructive
hydrocephalus. However, at present, plain and contrast-enhanced computed
tomography (CT) scans, with or without reconstruction (sagittal and coronal),
are sufficient to make the diagnosis of a mass in the region of the pineal
gland. In the last 20 years, magnetic resonance imaging (MRI) has proved to be
the most informative imaging procedure for determining the anatomical
localization of the mass, its relationship to adjacent vascular structures, and
its spread by either direct invasion or subarachnoid dissemination. Both CT and
MRI, while diagnostically highly accurate in determining the presence of a
pineal region mass, lack specificity as to the histological nature of the tumor.
Some relative specificity can be gained by paying attention to the density of
the tumor on CT, the enhancement of the tumor on CT and MRI, and the intensity
of the tumor on MRI. New in the diagnostic armamentarium is magnetic resonance
spectroscopy. The role of magnetic resonance spectroscopy in the evaluation of
pineal region tumors is, at present, relatively unknown but promising. Cerebral
angiography retains a role in the evaluation of pineal region masses only in
defining the arterial anatomy and venous relationships, information that may be
useful when surgical resection is contemplated. Occasionally, characteristics of
blood supply, such as dural tentorial blood supply (tentorial meningioma) may
indicate the likely histological nature of the lesion.

Plain Roentgenography

A normal pineal gland measures 5
to 9 mm in length, 3 to 5 mm in height and up to 6 mm in width. The calcified
pineal gland that is larger than 1 cm in any dimension should be looked upon
with suspicion. Not only the size of the pineal calcification and its location
are important but also the age at which the calcification appears. In the
literature on the evaluation of skull roentgenograms it had generally been held
that calcification of the pineal gland under the age of 10 was abnormal.
However, Schey found that physiologic calcification could be seen in persons as
young as 6 years. The overall incidence of calcification in childhood has been
given by Willich et al. as 0.83 percent and by Peterson and Kieffer as 5.1
percent.

It is clear from the literature
on pineal calcification detected on skull roentgenograms that the incidence
varies according to the age of the population examined, the quality of the
examination, and the genetic makeup of the population. The overall incidence of
pineal calcification is around 13 percent.

Another factor in the incidence
of skull radiographic evidence of pineal calcification is genetics. There is a
body of literature that gives different rates for pineal calcification,
according to the country of origin. Thus the incidence for Nigerians has been
reported as 5 percent, for Japanese as 9.9 percent, for Fijians as 15 percent
and for Indians as 19 to 24 percent. In contrast to these reports are the
similar incidences found for calcification per decade of life by Adeloye and
Felson in the American population and by Bhatti and Khan in the Pakistani
population. For the first decade of life the incidence was zero in both series,
for the second decade it was between 1.5 and 2.3 percent and for the third
decade it was 10.5 percent. The incidence of pineal calcifications in both
Americans and Pakistanis rises to 30 percent as the population ages into the
middle and later years.

Roentgenograms of the skull may
be of diagnostic value in the patient with a pineal tumor if (1) the tumor
produces calcification that is visible on the skull films; (2) the pineal tumor
produces obstructive hydrocephalus with increased intracranial pressure that
demineralises the floor of the sella or separates the sutures or the dilated
third ventricle amputates the dorsum sellae; or (3) the obstructive
hydrocephalus causes inferior and posterior displacement of the pineal
calcification(s).

The frequency of positive plain
skull films in a series of pineal tumors varies. Abay et al., in a series of 24
patients with pineal tumors, found that in 25 percent the skull roentgenograms
were abnormal on the basis of pineal tumor calcification, pineal calcification
position, or evidence of increased intracranial pressure. Lin et al. reported a
series of 32 pineal neoplasms, with calcifications seen in the region of the
pineal in 75 percent. Of those with pineal calcification, the pineal gland was
abnormal in size in 21 percent and in an abnormal position in 67 percent. The
presence of the pineal calcification was abnormal in four of five patients who
were 5 years of age or under (80 percent). The histologic classification of the
tumors in the patients with abnormally large pineal calcification was teratoma
in two, atypical teratoma in one, and pineoblastoma in two.

Computed Tomography

Factors that affect the
detection of pineal calcification by CT are the thickness of the CT section, the
size of the gland, the portion that is calcified, and the density of the
calcification. Denser calcifications, thinner sections, and greater calcific
portions make identification easier. It has been demonstrated that 8-mm-thick CT
sections are eight times more sensitive than skull roentgenograms in the
detection of 3-mm calcifications and 22 times more sensitive for 10-mm
calcifications.

The youngest patient with a
normally calcified pineal gland on CT was age 6.5 years in the series of
Zimmerman and Bilaniuk. In this series, from ages 8 to 14 years the incidence of
pineal calcification ranged between 8 and 11 percent. At age 15 the incidence
rose to 30 percent, and at age 17, to 40 percent. Thus, the incidence of pineal
calcification as detected by CT shows an increase that coincides with the onset
of puberty. The presence of a small pineal calcification on CT, in and of
itself, from age 6.5, upward is not evidence of a pineal neoplasm. Calcification
under age 6 should be looked upon with suspicion.

CT has become an important
diagnostic test for demonstrating the presence or absence of a pineal tumor. In
the series of Abay et al. eight of nine CT studies were positive for pineal
tumors. In one instance the CT was thought to be normal. In this false-negative
study done on a first-generation CT scanner, the image quality was not ideal. In
the first 44 pineal neoplasms diagnosed in the author's department since the
advent of CT, there were two instances (4.5 percent) in which the pineal tumor
was not appreciated initially. In one case. a 12-year-old girl presented with
abnormal contrast enhancement of the subarachnoid space and a normal pineal
region. Several subsequent CT examinations showed the same findings. Eight
months after the onset of her headaches, a high-resolution. thin-section CT
examination revealed a small pineal tumor. Biopsy revealed a pineoblastoma
(primitive neuroectodermal tumor) and examination of the subarachnoid space
revealed evidence of tumor seeding. The other patient had previously been
treated for bilateral retinoblastomas. He was found to have an "incidental" CT
finding of a pineal calcification at age 2 months. The patient was followed for
a year, during which time a soft tissue mass grew around the calcification,
producing obstructive hydrocephalus. Biopsy of this mass revealed a
pineoblastoma. The first case represents a false-negative CT examination due to
the small size of the lesion, while the second case represents a failure to
appreciate the significance of a too-early-appearing pineal calcification.

Thirty-one patients with pineal,
parapineal or histologically related tumors were reported by Zimmerman et al.
The CT characteristics in that series allowed differentiation between benign
(germinal) tumors, such as teratomas and epidermoids from malignant germinal
tumors, such as the germinoma and embryonal cell carcinoma. Primary pineal
tumors (pineoblastoma, pineocytoma) could not be differentiated from malignant
germinal tumors on the basis of CT criteria alone. Germinomas appeared as soft
tissue masses of slightly greater density than normal brain tissue.
Calcification was not a feature of the tumor matrix in germinomas. Frequently
the germinoma surrounded a centrally placed normal-appearing pineal
calcification. In the smaller tumors, the germinoma was well defined and did not
appear to invade the surrounding brain or subarachnoid spaces. Uniform contrast
enhancement was the rule. With larger germinomas the margins became poorly
defined and infiltration into the adjacent brain parenchyma and subarachnoid
spaces became more common. Cystic changes within a non-operated tumor were
unusual. Embryonal cell carcinomas had soft tissue densities similar to those of
the germinomas and they commonly contained tumor calcification; but in contrast
to the germinomas, the embryonal cell carcinomas more often showed cystic areas.
The benign teratomatous tumors also showed cystic areas. In addition, the benign
teratomatous tumors showed evidence of tissue derived from all three germinal
layers, such as calcification, ossification, teeth, fat and soft tissue
densities.

Epidermoid tumors of the pineal
region have a density in the range of cerebrospinal fluid (CSF) and do not
enhance with contrast administration. Thus, they may be confused with an
arachnoid cyst or encysted ventricular structures.

Both the pineocytomas and
pineoblastomas show an isodense to hyperdense tumor matrix, contrast enhancement
and a tendency toward parenchymal calcifications within the tumor matrix. Two
patients with pineoblastomas, when followed by sequential CT examinations prior
to treatment, showed rapid tumor growth. All but one of the pineoblastomas
presented within the first 12 years of life. The case in which the pineoblastoma
presented later at age 40, occurred in the mother of the child who had presented
at age 12 with a pineoblastoma. The increased incidence of pineoblastomas in
patients with congenital bilateral retinoblastomas and the occurrence of
pineoblastoma in mother and daughter raise the interesting question of a genetic
predisposition in at least some patients.

Astrocytomas that arise within
the pineal gland or adjacent to it will expand the gland, invade it or displace
it. Since a glial stroma supports the pineocytes and is an integral part of the
gland, some astrocytomas, presumably a small proportion of those involving the
gland, arise directly from the pineal gland. Most often these tumors are of
decreased density relative to brain parenchyma. The contrast enhancement that
occurs is usually inhomogeneous.

Calcification occurs
infrequently in these tumors, but when it does, its nature and position may make
the differential diagnosis between astrocytoma of adjacent structures and
non-astrocytic pineal tumor difficult. Because of their location, posterior
hypothalamic astrocytomas and astrocytomas of the tectum of the mesencephalon
may also be difficult to differentiate from primary pineal tumors on transverse
section CT. They frequently abut on the cerebral aqueduct or on the posterior
third ventricle, producing obstructive hydrocephalus similar to that produced by
a primary pineal neoplasm. To differentiate these tumors by location, careful
attention needs to be paid to the size and shape of the tectal region: the
radiologist needs to look for forward displacement of the calcified pineal gland
by an upper brain stem mass. Sagittally reconstructed sections may be of
particular advantage in this situation, as may be the use of a subarachnoid
non-ionic water soluble contrast agent at the time of CT sectioning.

In interpreting the CT findings,
attention should be paid to the patient's age and sex. Teratomatous tumors of
the pineal region occur almost exclusively in males. Germinomas occur in both
males and females, most frequently in the second and third decades. Embryonal
cell carcinoma occurs most often in the male in the second decade. Both
germinomas and embryonal cell carcinomas are radiosensitive, but only the
germinoma is radiocurable. After a period of regression, embryonal cell
carcinoma tends to recur promptly. Sex distribution in the
pineocytoma-pineoblastoma group seems equal. In a female patient with a
calcified tumor in the pineal region, the most likely diagnosis is a tumor of
primary pineal origin.

Cerebral Angiography

The major blood supply to the
pineal gland arises from the posterior medial choroidal artery, a branch of the
posterior cerebral artery. This vessel arises from the interpeduncular segment
of the posterior cerebral artery. extends superiorly through the cistern of the
lamina tecti and comes to lie on the lateral surface of the pineal gland. The
artery continues on past the pineal to supply blood to the choroid plexus in the
roof of the third ventricle. The pineal gland is drained by veins that originate
from its superior and inferior surfaces. These veins drain into either the
internal cerebral vein or the great vein of Galen. Superimposed upon the pineal
vein anatomy on the lateral vertebral angiogram are the thalamic veins. It is
difficult to differentiate pineal from thalamic veins. The internal cerebral
vein lies in the roof of the third ventricle and then extends posteriorly
through the velum interpositum into the cistern of the lamina tecti, where it
joins the opposite internal cerebral vein and, with both basilar veins of
Rosenthal, forming the vein of Galen. The vein of Galen lies just beneath the
splenium of the corpus callosum and extends posteriorly to join the inferior
sagittal sinus to form the straight sinus, which lies at the point of insertion
of the falx cerebri onto the tentorium.

In the pathologic situation, a
number of adjacent arterial and venous structures may be displaced or deformed
or may provide an abnormal source of blood supply or venous drainage. How often
these findings are appreciated angiographically is uncertain. It is probable
that the degree to which these findings are appreciated depends upon the quality
of the examination. A high-quality examination requires magnification
angiography with subtraction, following the delivery of an adequate volume of
contrast agent to the tumor bed in a patient who is able to cooperate. Abay et
al. in a series of 12 pineal tumors studied by angiography, reported the
presence of tumor vascularity or stain in four (33 percent).

More important than the presence
of tumor stain is the recognition of the displacement of adjacent arteries and
veins. Vascular displacements are dependent upon the direction of growth of the
neoplasm and upon enlargement of the ventricular system resulting from
obstruction of the posterior third ventricle or aqueduct. When the pineal gland
is enlarged, the posterior medial choroidal artery is displaced posteriorly and
laterally, and the superior and inferior pineal veins become more separated. The
internal cerebral vein, which lies just above the pineal gland, is impinged on,
elevated, and stretched. If the mass effect is sufficient, an angular deformity
occurs at the point of juncture between the internal cerebral vein and the vein
of Galen. If the tumor is large and extends posterolaterally, the vein of
Rosenthal can also be deformed. As the tumor extends back into the cistern of
the lamina tecti, down onto the tectum of the mesencephalon, and against the
anterior-superior vermis, other changes occur. The superior cerebellar arteries
are spread apart within the lamina tecti cistern (shown best with a Towne
projection of the vertebral arteriogram); the precentral cerebellar veins are
flattened and displaced from front to back (seen on the lateral projection of
the vertebral angiogram); and the superior cerebellar artery branches, as they
go over the anterior superior vermis, are flattened and deformed from front to
back (seen on the lateral projection of the vertebral arteriogram). If the tumor
extends forward (inferiorly), into the floor of the third ventricle, or as the
third ventricle dilates from obstructive hydrocephalus, the thalamic perforating
branches that arise from the proximal posterior cerebral arteries and posterior
communicating arteries are displaced and stretched (seen on the lateral
projection of the vertebral arteriogram). With obstructive hydrocephalus, the
posterior lateral choroidal arteries (branches of the posterior cerebral artery
that supply the choroid plexus of the lateral ventricles) are stretched. In the
rare instance of a parapineal tentorial meningioma, selective injection of the
internal carotid artery may show its dural blood supply, which is derived from
the intracavernous portion of the internal carotid artery through the tentorial
branch of the meningohypophyseal trunk. Both internal carotid arteriography and
vertebral arteriography are of use in the differential diagnosis of pineal
neoplasms when the lesion proves to be a vascular anomaly (such as a vein of
Galen aneurysm) that stimulates a pineal tumor on CT examination.